Field of the Invention
The present invention relates to a carburetor for a stratified scavenging engine suitable for a two-stroke internal combustion engine.
Background Art
Conventionally, in two-stroke internal combustion engines, a gaseous mixture, which has been pressurized in a crank chamber, is supplied to a combustion chamber of a cylinder through a scavenging hole, thereby scavenging combusted gas remaining in the combustion chamber of the cylinder.
To improve scavenging of the combustion gas, the gaseous mixture which has flowed into the combustion chamber is emitted into the atmosphere through the emission hole together with the combusted gas, a phenomenon called blow-by, and this increases the amount of uncombusted components in gas emissions, which is a waste of fuel.
Blow-by can be controlled by closing the emission hole earlier with the piston, but that simply increases the amount of combusted gas remaining in the combustion chamber of the cylinder, leading to imperfect combustion, which not only increases the amount of hydrocarbons in the gas emissions, but also reduces the overall output of the two-stroke internal combustion engine.
Accordingly, one known method for solving this problem is an engine wherein during the scavenging step of the two-stroke internal combustion engine leading air, which is introduced beforehand into a scavenging path or the like, and the gaseous mixture which follows flow into the cylinder in stratified layers from the scavenging port, which prevents uncombusted gas from flowing out of the emission port (i.e., blow-by) (a stratified scavenging two-stroke internal combustion engine).
With the carburetor connected to this stratified scavenging two-stroke internal combustion engine, when the crank chamber is in a negative pressure state when the piston is up, the gaseous mixture controlled by a rotary fuel control valve is drawn into the crank chamber through the intake hole while at the same time air controlled by a rotary air control valve is drawn from the air path into the scavenging path via a check valve.
When the gaseous mixture explodes the piston drops, the emission hole opens when the piston is at bottom dead center, the combusted gas is emitted, and then the scavenging hole opens, the air in the scavenging path is injected into the combustion chamber of the cylinder by the positive pressure in the crank chamber, and then the gaseous mixture in the crank chamber is injected into the combustion chamber.
While the emission hole is open, the air initially injected into the combustion chamber of the cylinder through the scavenging hole flows out to the emission hole, and the emission hole remains closed until the gaseous mixture flows to the emission hole.
Thus, in a two-stroke internal combustion engine to which the aforementioned carburetor is attached, only the air is scavenged, making it possible to control blow-by of the gaseous mixture.
However, in the case of a carburetor (FIG. 5) which is connected to a typical two-stroke internal combustion engine using a rotary valve as shown in FIG. 6, the fuel intake path and the air path are disposed in parallel, the rotary valve which is used in flow rate control in these paths is disposed so as to pass perpendicularly through the fuel intake path and the air path, allowing coaxial adjustment of the flow rate along both the fuel intake path and the air path by the rotary valve. This makes it difficult to establish airtightness between the fuel intake path and the air path independently of one another. When the negative pressure from the two-stroke internal combustion engine acts inside the carburetor, part of the fuel in the fuel intake path is drawn into the air path through a gap between the rotary valve and the valve hole, preventing stable supply of air and fuel and rendering performance of the internal combustion engine unstable, which is a factor causing the engine to stall.
Relative to this problem, JP 2000-352354 A discloses a carburetor for a two-stroke internal combustion engine whereby the negative pressures from the two stroke internal combustion engine which acts on the rotary fuel control valve and the rotary air control valve do not interfere with one another in the carburetor.
Specifically, by disposing a sealing member between the outer circumference of the rotary air control valve and the cylindrical portion into which the rotary air control valve is inserted, or between the outer circumference of the rotary fuel control valve and the cylindrical portion into which the rotary fuel control valve is inserted, and maintaining airtightness between the fuel intake path and the air path, interference between the negative pressure from the two-stroke internal combustion engine acting on the rotary fuel control valve and the rotary air control valve can be prevented inside the carburetor.
On the other hand, a method whereby a sealing member maintains airtightness with the outer circumference of the cylindrical portion of the rotary air control valve and the rotary fuel control valve is very effective in terms of maintaining airtightness of the paths, but since the sealing member needs to be disposed, the number of parts needed for the carburetor increases, which causes the cost to rise. Moreover, as a result of continuous use, the sealing member wears down and swells, which can become a factor in malfunctions due to a drop in airtightness.